1. Field of the Invention
This invention relates generally to the field of indicating a point of contact between two objects. In a particular embodiment, the invention relates to a ball treated so as to leave a transient visible mark at the point of contact with a surface.
2. Background
A number of games, particularly tennis, are played on a court marked with boundary lines. During playing of the game, it is important to know when a ball lands outside of the boundary lines since this will affect the scoring of the game. In games where the ball is traveling at high speed, it is frequently difficult to visually determine if the ball has landed “in” or “out” of bounds. Line judges are typically employed in professional matches to make such determination. Their calls are important to the outcome of the game and often incite heated reaction from the players and spectators.
A number of methods and systems have been proposed for automatically determining whether a game ball, particularly a tennis ball, is “in” or “out”. Many of these require specially prepared courts and/or sophisticated tracking equipment. A system described in U.S. Pat. No. 4,109,911 utilizes a ball with a chemically treated surface that provides a transient indication when it contacts a chemically treated court surface. Thus, even this system requires a specially prepared court.